Dielectric fluids are non-conducting fluids used in a variety of applications. Those applications include transformers, capacitors, switching gears, transmission components, distribution components, switches, regulators, circuit breakers, autoreclosers, and other electrical apparatus and electrical components.
Dielectric fluids are particularly useful in transformers. When transformers are operating, the power losses occur and manifest as heat. To prevent excessive temperature rise, transformers are filled with dielectric fluids to dissipate the relatively large quantities of heat generated.
In a transformer, the dielectric fluid also provides electrical insulative properties to the internal transformer components. Notably, transformers contain electrical insulation which is utilized to prevent energized components or conductor from contacting or arcing over the other components, conductor or other internal circuitry. Heat degrades insulation. High temperatures can shorten the life of insulation.
Accordingly, thermal management of a transformer is critical to the safe operation of the transformer.
Thermal stability of the dielectric fluid is also important because of the desired service life of a transformer. For example, it is desirable that a transformer have a service life of over twenty (20) years. The dielectric fluid must be thermally stable so that it may dissipate heat and protect the insulation for more than 20 years.
Polychlorinated biphenyl compounds (also known as “PCBs”), once used as dielectric fluid in transformers, have been phased out due to their toxic properties and negative environmental impact. Non-toxic transformer oils that have replaced PCBs include fatty acid esters, fluorinated hydrocarbon oils, microbial oil, mineral oils, silicone-based hydrocarbon oils, vegetable-based oils, and vegetable seed oils. These non-toxic oils have drawbacks regarding viscosity, flash point, fire point, pour point, water saturation point, dielectric strength and/or other properties limiting their usefulness as dielectric fluids.
For example, vegetable oils are friendly to the environment, have excellent dielectric characteristics, high temperature stability, superior flash and fire resistance, and are compatible with solid insulating materials. However, vegetable oils have high pour point, thereby yielding a typical temperature operating window of vegetable oil-based dielectric fluids −15 degrees Celsius to 110 degrees Celsius. Additionally, when compared to mineral oils, vegetables are more viscous and less thermally stable.
Mineral oil-based dielectric fluids are not free of concerns. A key disadvantage of mineral oil is its fire point near at 150 degrees Celsius, which is much lower than that of the vegetable oil or other less flammable fluids such as silicon oil.
Consequently, a need exists for a non-toxic, biodegradable, PCB-free dielectric fluid for electrical components that have the same, or substantially the same, chemical, mechanical, and/or physical properties as PCB-based dielectric fluid.